Solid-state thermoelectric converters are recently receiving increasing attention due to their potential to make important contributions to the effort on reducing CO2 and greenhouse gas emission and providing cleaner forms of energy. Such converters utilize thermoelectric materials, that is, materials that show the thermoelectric effect in a strong and/or convenient form. Thermoelectric effects involve direct conversion between thermal and electrical energy by employing electrons and holes as the energy carriers, which can be used, for example, for waste heat recovery, and for thermal management of microelectronics and biological systems. A good thermoelectric material has high dimensionless figure-of-merit ZT: defined as (S2σ/κ)T, where the S, σ, κ, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Numerous efforts have been devoted in the last two decades in order to increase the ZT value from the longstanding 1.0 in thermoelectric bulk materials to higher values.